1. Field of the Invention
The present invention relates to a semiconductor device socket for connecting an external circuit to external leads of a surface package type semiconductor device in order to test the device.
2. Description of the Related Art
FIGS. 13 and 14 are sectional views illustrating the basic structure of a conventional semiconductor device socket. FIG. 13 illustrates a state where movable contact terminals of the socket are open, and FIG. 14 illustrates a state where the movable contact terminals are closed. FIG. 15 is a partial perspective view illustrating only a portion near a semiconductor device which is mounted on a socket. In FIGS. 13, 14 and 15, reference numeral 1 denotes a surface package type semiconductor device (referred to as IC hereinafter); reference numeral 2, a plurality of gull wing-like external leads which extend from both sides of the IC 1, as shown in FIG. 10; and reference numeral 3, a package portion. Each of the external leads 2 has a shoulder 4, a flat end 5, a mounting surface 6 on the rear side of the end 5, and an upper surface 7 on the front side thereof. The mounting surface 6 contacts an electrode (not shown) on a circuit substrate when the IC 1 is actually mounted on the circuit substrate.
Reference numeral 50 denotes a semiconductor device socket comprising a body 20 for mounting the IC 1 thereon, and a movable cover 40 which is provided on the body 20 so as to be vertically movable.
The body 20 has a positioning base 21 for supporting the package portion 3 of the IC 1 and positioning the IC 1, terminal guides 22 for guiding the ends 5 of the external leads 2 of the IC 1 and aligning the movable contact terminals 30 described below, and a lead end supporting surface 23 for supporting the mounting surface 6 of each of the external leads 2. Reference numeral 30 denotes the movable contact terminal provided in correspondence with each of the external leads 2. The movable contact terminals 30 are provided in a row on both sides of the positioning base 21 outside the positioning base 21 in correspondence with the respective external leads 2, and the terminal guides 22 are provided between the respective movable contact terminals 30. In a socket for a QFP (Quad Flat Package) type semiconductor, the movable contact terminals 30 are provided on each of the four sides. Each of the movable contact terminals 30 has a lever portion 31, a contact portion 32, and a terminal portion 33 for electrical connection with an external circuit (not shown).
The movable cover 40 has an opening 41 for getting the IC 1 in and out of the socket 50, the IC 1 being mounted on the positioning base 21 through the opening 41 while the external leads 2 are respectively guided by the terminal guides 22. The movable cover 40 also has an engagement portion 42 on the rear side thereof, which has an arcuate surface 43 contacting the lever portion 31 of each of the movable contact terminals 30 to open and close each of the movable contact terminals 30 as the movable cover 40 is vertically moved.
The operation of the conventional semiconductor device socket is described below.
When the movable cover 40 of the socket 50 is downwardly moved to engage the body 20, as shown in FIG. 13, the lever portion 31 of each of the movable contact terminals 30 is forced open by the arcuate surface 43 on the rear side of the movable cover 40, and the contact portion 32 is upwardly retracted along a circular arc. In this state, the IC 1 is mounted on the positioning base 21 of the body 20, as shown in FIG. 13.
When the pressure pushing down the movable cover 40 is removed, each of the movable contact terminals 30 made of an elastic metal material such as BeCu or the like is returned to the closed state by its own elastic force, and the contact portion 32 consequently pushes the upper surface 7 at the end 5 of the corresponding external lead 2 of the IC 1. At the same time, the movable cover 40 is pushed up by the elastic force of each of the movable contact terminals 30 and separated from the body 20. In this state, the contact portion 32 of each of the movable contact terminals 30 pushes the upper surface 7 at the end 5 of the corresponding external lead 2 supported on the lead end supporting surface 23 of the body 20, as described above, thereby achieving electrical connection between the movable leads 2 and the respective corresponding external leads 2. The above operation causes the IC 1 to be mounted on and separated from the socket 50 in order to perform tests such as the electrical characteristic test and burn-in screen test of the IC.
In the conventional semiconductor device socket configured as described above, the ends of the external leads of the IC respectively electrically contact the movable contact terminals on the socket side. However, since a solder coating (not shown) is previously placed on the end of each of the external leads when the IC is mounted on the circuit substrate, and since the lead end contacts directly an electrode on the circuit substrate when the IC is mounted on the circuit substrate, and is thus required to be planar, it is undesirable that the ends of the external leads make electrical contact. This is due to the following problems:
(1) If the lead ends make electrical contact, since the contact terminals on the socket side are pressed, the solder coating is separated.
In addition, when an IC having resin burrs which adhere to portions between the respective external leads is mounted on the socket in order to perform function tests in the course of the production of the IC or immediately after the production, various foreign materials A such as the mold burrs separated from the portions between the external leads of the IC package portion, fiber flocks of the clothing of the workers etc. in the room remain and are deposited on the body including the lead end supporting surface 23 of the socket, as shown in FIG. 15. If the mounting surfaces at the ends of the external leads of the IC are pressed on the surface of the body of the socket in this state, the foreign materials A sometimes adhere to the mounting surfaces of the external leads. This causes the following problems:
(2) When a test for electrical connection of the mounting surfaces of the external leads is then performed, or when the IC is actually mounted on the circuit substrate, the foreign materials which adhere to the mounting surfaces cause poor electrical contact; and
(3) Since a force is applied in the state where the foreign materials adhere, the lead ends are deformed, as shown by portion B in FIG. 15, thereby causing a defective product.